1. Field of the Invention
The invention concerns water-based inks and ink sets and use thereof for writing, drawing, painting, printing and specifically also for ink jet printing and other machine writing, printing, painting or labeling processes, where the inks are preferably applied to coated media.
2. Description of Related Art
In principle, such inks and ink sets are known, e.g., for ink jet printers. For example, European Patent No. 526 731 B1 describes an ink jet ink set with red (magenta), blue (cyan) and yellow ink for use in ink jet printers.
In this process, 1.75% to 4% dyestuffs selected from the following groups are added to a vehicle consisting of 5% to 11% glycols and/or glycol ethers and water: Reactive Red 180, Acid Red 52, Acid Yellow 23 and/or Acid Blue 9.
One disadvantage of this process in particular is that whether mixed or used individually, these inks and their impressions do not have good lightfastness or uniform, i.e., equal, rates of fading.
European Patent No. 0 345 763 B1 discloses printing ink solutions that are said to yield especially bright, lightfast, and moisture-resistant impressions. These printing ink solutions, which are to be used in particular to produce magenta or blue ink, essentially contain at least two different dyestuffs. Each of these dyestuffs is produced or formulated according to specific requirements, and at least one other dyestuff (according to C.I.=Color Index) is a dyestuff to be selected from the group: Acid Red 131, Acid Red 274, Direct Red 227, Direct Red 9, Direct Yellow 86, Direct Yellow 142, Direct Blue 199, Direct Blue 86 and/or Acid Blue 198. The proposed dyestuffs should be dissolved or dispersed in a liquid medium, where the solvent should include a polyhydric alcohol or an aliphatic monohydric alcohol.
A disadvantage of these printing ink solutions is that one of the dyestuffs contained in each ink is not a conventional commercial product and therefore is not readily available. Furthermore, a plurality of dyestuffs mixed together are always required, so that, first, it is not necessarily always possible to manufacture inks and, second, they are very expensive. Furthermore, it is not readily apparent how the individual inks of a complete ink set consisting of at least three different ink colors can or should be prepared, or whether or how it is possible to guarantee good lightfastness and relatively uniform color constancy even with mixed colors.
In addition, there are known pigment inks with a relatively high lightfastness on the market, but they sediment readily and do not have a long shelf life and they also frequently cause blockage of extremely fine capillaries and nozzles of the reservoirs and/or printing wicks or ink jet heads. Such pigment inks have previously been considered the most lightfast inks of all, and it seemed practically impossible or extremely difficult to obtain comparable good values with dyestuff inks.